This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Silk is a biopolymer with high mechanical performances produces in vivo in environment-friendly conditions. In order to mimic the natural process of silk formation, the effect of each parameter involved in it must be understood. We built a microfluidic chip enabling us to study both the effect of ionic composition of the protein solution and shear forces applied to it along its transformation to a solid fiber. In this project, we intend to follow by small-angle x-ray scattering (SAXS), the evolution of the silk protein structure along its pathway in this x-ray transparent chip. Preliminary results showed that cations such as copper and calcium trigger silk protein (fibroin) aggregation but in a different way. We have seen by single-fiber diffraction experiments that in certain conditions, the fiber produced in the chip has a semi-crystalline structure characteristic of natural silk. These complementary results are very promising and in situ SAXS measurements are now required to further improve our comprehension of the effect of each parameter.